fossil: Explicitly link with libm

Fixes the following build error with an external toolchain:

./bld/sqlite3.o: In function `fts5Bm25Function':
sqlite3.c:(.text+0x27234): undefined reference to `log'
./bld/piechart.o: In function `piechart_render':
piechart_.c:(.text+0x430): undefined reference to `sincos'
piechart_.c:(.text+0x47c): undefined reference to `sincos'
piechart_.c:(.text+0x548): undefined reference to `sincos'
collect2: error: ld returned 1 exit status
src/main.mk:526: recipe for target 'fossil' failed
make[3]: *** [fossil] Error 1

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

net/fossil/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=fossil
 PKG_VERSION:=1.34
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_LICENSE:=BSD-2-Clause
 PKG_MAINTAINER:=Luka Perkov <luka@openwrt.org>
@@ -42,7 +42,7 @@ endef
 MAKE_FLAGS := \
 	TCC="$(TARGET_CC)" \
 	CFLAGS="$(TARGET_CFLAGS) -I$(STAGING_DIR)/usr/include -DFOSSIL_ENABLE_JSON" \
-	LDFLAGS="$(TARGET_LDFLAGS) -Wl,-rpath=$(TOOLCHAIN_DIR)/lib -L$(STAGING_DIR)/lib -L$(STAGING_DIR)/usr/lib" \
+	LDFLAGS="$(TARGET_LDFLAGS) -Wl,-rpath=$(TOOLCHAIN_DIR)/lib -L$(STAGING_DIR)/lib -L$(STAGING_DIR)/usr/lib -lm" \
 
 define Build/Configure
 endef